An image reading device includes a conveying unit, reading unit, detecting unit, and control unit. The conveying unit conveys two sheets of the original one by one. The reading unit reads a sheet passing past a reading position. The detecting unit detects a sheet passing past a detection position upstream of the reading position in a conveying direction. The control unit controls the reading unit to start a reading process when a leading edge of sheet reaching a position upstream of the reading position by a first distance, controls the reading unit to stop the reading process when a trailing edge of sheet reaching a position downstream of the reading position by a second distance, determines an interspace between the trailing edge of sheet and a leading edge of a subsequently-conveyed sheet, and updates the first distance and the second distance based on the interspace.